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defmodule Cepis.HTTP do
@moduledoc false
alias Cepis.Client
alias Cepis.{NetworkError, RateLimitError, ServerError}
@retriable_status [429, 500, 502, 503, 504]
@accept ~c"application/json, text/csv;q=0.9, */*;q=0.1"
@epoch_offset 62_167_219_200
@spec request(Client.t(), String.t(), [pos_integer()]) ::
{:ok, pos_integer(), binary(), list()} | {:error, Cepis.Error.t()}
def request(%Client{} = client, path, accepted \\ [200]) do
url = client.base_url <> path
deadline =
if client.total_timeout, do: monotonic() + client.total_timeout
attempt(client, url, accepted, 1, deadline, nil)
end
defp attempt(client, url, accepted, number, deadline, last) do
if expired?(deadline) do
give_up(client, url, last)
else
case get(client, url) do
{:ok, status, body, headers} ->
if status in accepted or status not in @retriable_status do
{:ok, status, body, headers}
else
next(client, url, accepted, number, deadline, {:status, status, retry_after(headers)})
end
{:error, reason} ->
next(client, url, accepted, number, deadline, {:network, reason})
end
end
end
defp next(client, url, accepted, number, deadline, last) do
if number >= client.max_attempts do
give_up(client, url, last)
else
case wait_for(client, number, deadline, last) do
:expired ->
give_up(client, url, last)
milliseconds ->
Process.sleep(milliseconds)
attempt(client, url, accepted, number + 1, deadline, last)
end
end
end
defp wait_for(client, number, deadline, last) do
wait = backoff(client, number, requested_wait(last))
case deadline do
nil ->
wait
_ ->
remaining = deadline - monotonic()
if remaining <= 0, do: :expired, else: min(wait, remaining)
end
end
defp requested_wait({:status, _status, retry_after}), do: retry_after
defp requested_wait(_), do: nil
defp backoff(client, _number, retry_after) when is_integer(retry_after) do
min(retry_after, client.backoff_max)
end
defp backoff(client, number, _retry_after) do
ceiling = min(client.backoff_base * Integer.pow(2, min(number - 1, 30)), client.backoff_max)
trunc(:rand.uniform() * ceiling)
end
defp get(client, url) do
ensure_started()
request = {String.to_charlist(url), headers(client)}
http_options =
[
timeout: client.timeout,
connect_timeout: client.timeout
] ++ tls_options(url)
case :httpc.request(:get, request, http_options, body_format: :binary) do
{:ok, {{_version, status, _reason}, headers, body}} -> {:ok, status, body, headers}
{:ok, {status, body}} -> {:ok, status, body, []}
{:error, reason} -> {:error, reason}
end
end
defp headers(client) do
[
{~c"user-agent", String.to_charlist(client.user_agent)},
{~c"accept", @accept},
{~c"accept-encoding", ~c"identity"}
]
end
defp tls_options("https://" <> _rest) do
[
ssl: [
verify: :verify_peer,
cacerts: :public_key.cacerts_get(),
depth: 3,
customize_hostname_check: [
match_fun: :public_key.pkix_verify_hostname_match_fun(:https)
]
]
]
rescue
_ -> []
end
defp tls_options(_url), do: []
defp ensure_started do
{:ok, _} = Application.ensure_all_started(:inets)
{:ok, _} = Application.ensure_all_started(:ssl)
:ok
end
defp retry_after(headers) do
case header(headers, "retry-after") do
nil -> nil
value -> parse_retry_after(String.trim(value))
end
end
defp parse_retry_after(value) do
case Float.parse(value) do
{seconds, ""} -> max(0, trunc(seconds * 1000))
_ -> parse_http_date(value)
end
end
defp parse_http_date(value) do
case :httpd_util.convert_request_date(String.to_charlist(value)) do
:bad_date ->
nil
datetime ->
target = :calendar.datetime_to_gregorian_seconds(datetime) - @epoch_offset
max(0, (target - System.os_time(:second)) * 1000)
end
end
defp header(headers, name) do
Enum.find_value(headers, fn {key, value} ->
if key |> to_string() |> String.downcase() == name, do: to_string(value)
end)
end
defp give_up(client, url, {:status, 429, retry_after}) do
{:error,
%RateLimitError{
message: "rate limit reached at #{url} (after #{client.max_attempts} attempt(s))",
retry_after: retry_after
}}
end
defp give_up(client, url, {:status, status, _retry_after}) do
{:error,
%ServerError{
message: "the API answered #{status} at #{url} (after #{client.max_attempts} attempt(s))",
status: status
}}
end
defp give_up(client, url, {:network, reason}) do
{:error,
%NetworkError{
message:
"could not reach #{url} (after #{client.max_attempts} attempt(s)): #{inspect(reason)}",
reason: reason
}}
end
defp give_up(_client, url, nil) do
{:error,
%NetworkError{
message: "gave up on #{url}: total_timeout elapsed before any attempt completed",
reason: :timeout
}}
end
defp expired?(nil), do: false
defp expired?(deadline), do: monotonic() >= deadline
defp monotonic, do: System.monotonic_time(:millisecond)
end
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